“A fossil is the remains of something that was once alive, plant or
animal,” says Mike Benton. He’s a paleontologist at the University of
Bristol in England.
Fossils typically form when an animal dies and its skeleton is covered with sediment such as sand or mud. As time passes, the sediment around the bone turns to rock. The bone dissolves, leaving behind a bone-shaped mold. This cavity gradually fills with minerals. The minerals harden in the shape of the original bone, forming a fossil.
Most fossils are bones. But if conditions are just right, fossils of more fragile material can be preserved too. Scientists have found fossils of everything from feathers to fish scales to poop!